Stepping motors may be used for accurate and exact movement of movable parts in machine tools, printers and other apparatus. In the case of printers it is also known to use a linear stepping motor with an armatur provided with magnetizing windings for the linear movement of the printing head, the armature being mounted on the same carriage as the printing head. By the individual magnetizing windings being here disposed after each other in the travelling direction of the armature, the armature elements will be short with consequently weak power. Another problem is also the limitation which the printing head-carrying armature of the stepping motor signifies for the acceleration capacity of the printing head, due to the weight of the iron cores and windings carried by the armature and the current supplying conductors to the windings which must also be moved. It is thus a desire to enable the implementation of the armature without windings, and instead place the windings with the stator, since such an arrangement enables a minimization of the weight and length of movable parts while maintaining a high quotient of force/mass. However, it has been difficult to find a suitable design of the stepping motor stator and armature for this purpose, since demands of placing the windings so that they do not obstruct the travel of the armature and the ncessity of restricting magnetic leakage losses have so far not been able to be combined in a satisfactory manner with other desirable properties of the apparatus.
An apparatus of the kind defined in the introduction, where the armature lacks a magnetizing winding, is known from FIGS. 1 and 2 in the Swedish patent application 7102912-8. Here the armature is implemented in the form of an elongate bar of magnetic material with a length greatly exceeding the combined length of the three stator elements disposed in register with each other along the direction of travel of the bar. The known apparatus is intended for numerically controlled machine tool applications where the great length of the bar is no disadvantage, due to the design principle used. For reasons which will be understood, the mentioned design principle is not suitable for applications where a small and light object, such as a printing head, is to be moved linearly within a limited space and be capable of rapid accelerations and decelerations.